1. Field of the Invention
The present invention relates to a driving apparatus of an image pick-up device which can be advantageously used in an electronic still camera.
2. Description of the Related Art
In FIG. 11 which shows a block diagram of a known electronic still camera, a lens 1 forms an image by receiving light from an object (not shown) to be captured on a CCD 3 through a diaphragm 2. A record/play-back portion 4 modulates picture signals (luminance signal and color signal) output from the CCD 3 to record it on a magnetic disc 5.
A photometering element 6 receives light from the object to output electrical signals to a photometering portion 7. The output of the photometering portion 7 is sent to a micro processing unit (MPU) 8. A release switch 9 is actuated to take a picture. A clock generator 10 for driving the CCD 3 is controlled by the MPU 8 to output clock signals CV1.about.CV4 for driving the CCD 3 and various timing signals. A multiplexer 11 selects one of the clock signals PV1.about.PV4 from the MPU 8 and the clock signals CV1.about.CV4 from the clock generator 10 to output clock signals V1.about.V4.
A driver 12 produces clock signals .PHI.V1.about..PHI.V4 for driving the CCD 3 from the clock signals V1.about.V4 input thereto from the multiplexer 11. One of a transfer clock signal CTG output from the clock generator 10 and a compulsive transfer clock signal PTG output from the MPU 8 is selected by an accumulation control selecting switch 13 to output it to the driver 12. The diaphragm 2 is controlled to open and close by a driving circuit 14.
The image pick-up operation of the electronic still camera mentioned above is as follows (FIGS. 12 and 13). The image pick-up operation is generally controlled by the MPU 8.
When the release switch 9 is made ON, the signal from the photometering element 6 is detected by the photometering portion 9 to output a signal corresponding to the luminance of the object to the MPU 8. The MPU 8 performs an arithmetic operation to obtain a numerical aperture Av and electronic shutter speed (period) Tv in accordance with the signal input thereto from the photometering portion 7, as shown at (a) and (c) in FIG. 12.
The timing generator 10 periodically outputs the clock signals CTG (FIG. 12(k)) at 1/60 second interval, in synchronization with the vertical synchronous signal VD (FIG. 12(b)). The MPU 8 outputs the switching signal Ps (FIG. 12(h)) of logic "H", and accordingly, the selecting switch 13 connects the terminal of the signal CTG to the terminal of the driver 12, so that the signal CTG is supplied to the driver 12 (FIG. 12(d)). The multiplexer 11 selects the clock signals CV1.about.CV4 output from the clock generator 10 to output the clock signals V1.about.V4 to the driver 11 when the switching signal Ps is logic "H".
The driver 12 produces clock signals .PHI.V1.about..PHI.V4 (FIG. 13(f).about.(i)) for driving the CCD 3 in accordance with the clock signals V1.about.V4 and the clock signal TG (or CTG or PTG) (FIGS. 13(a).about.(e)).
The clock signals .PHI.V1.about..PHI.V4 consist of three-valued levels VH, VM and VL. When the clock signals are level VH, the electrical charges are transferred to the vertical transfer CCD's from photo diodes which constitute the CCD 3. When the clock signals are level VM or VL, the charges of the vertical transfer CCD's are transferred to the horizontal transfer CCD or a sweeping drain. The direction of the transfer is controlled by the phase of the clock signals .PHI.V1.about..PHI.V4.
Thus, the unnecessary charges which are accumulated in the period TVn are transferred to the vertical transfer CCD's in accordance with the clock signal CTG, and are then swept therefrom through the sweeping drain in accordance with the clock signals .PHI.V1.about..PHI.V4, as shown in FIG. 12(d).
The MPU 8 controls the drive circuit 14 to open the diaphragm 2 at a predetermined numerical aperture obtained thereby (FIG. 12(e)).
Upon the completion of the sweeping of unnecessary charges and the setting of the diaphragm 2, the signal Ps is inverted to logic "L", in synchronization with the vertical synchronous signal, as shown in FIG. 12(h). As a result, the multiplexer 11 selects the clock signals PV1.about.PV4 from the MPU 8 to output it to the driver 12. The selection switch 13 is switched to connect to the terminal of the driver 12 to the terminal of the signal PTG. The MPU 8 generates the clock signal PTG at a time in which the interval of the two adjacent clock signals CTG is identical to the arithmetically obtained period Tv, as shown in FIGS. 12(d) and (j).
The charges accumulated in the photo diodes of the CCD 3 are transferred to the vertical transfer CCD's and thereafter, the charges corresponding to the quantity of light of the object are accumulated during the period Tv.
The MPU 8 inverts the signal Ps to logic "H" during the period Tv synchronously with the vertical synchronous signal in the period Tv to output the signal PVH to the clock generator 10, to thereby output the high speed sweeping clock signals CV1.about.CV4. As a result, the unnecessary charges which are transferred to the vertical transfer CCD's and which are accumulated during the period Tvn+1 are swept through the sweeping drain at a high speed (FIG. 12(d)).
Upon the completion of the high speed sweeping, the charges of the photo diodes are transferred to the vertical transfer CCD's in accordance with the clock signal CTG. The signal Ps is again inverted to "L", as shown in FIG. 12(h). Then, the diaphragm 2 is driven to close (FIG. 12(e)). Consequently, relatively intensive light is incident upon the CCD 3 after the lapse of the period Tv, so that the charges produced by the photo diodes leak out into the vertical transfer CCD's 3 to prevent the occurrence of smear.
After the diaphragm 2 is closed, the signal REC is output from the MPU 8 to the record/play-back portion 4 and the magnetic disc 5. Also, the signal Ps becomes "H", and the signal PHV becomes "L", respectively (FIGS. 12(f), (h) and (i)). Consequently, the clock signal CV1.about.CV4 are output again from the clock generator 10 at low speed, so that the signals are read from the vertical transfer CCD's through the horizontal transfer CCD to be supplied to the record/play-back portion 4. Thereafter, the record/play-back portion 4 performs an FM-modulation of the signals to output the modulated signals to the magnetic disc 5 to be recorded, as shown in FIGS. 12(d), (f) and (g).
As can be seen from the foregoing, since the charges which are accumulated during the operation of the electronic shutter are transferred and read when the diaphragm 2 is closed, no smear occurs.
However, if a relatively intensive light is incident before the diaphragm 2 is closed, the charges overflow from the photodiode into other photodiode or the vertical transfer CCD's, so that a so-called blooming phenomenon occurs, as shown in FIG. 14.